1. Field of the Invention
The present invention relates to an observing apparatus for use in microscopes and more particularly to autofocus mechanism to be used for observation and others.
2. Description of Related Art
There have been known the following two methods of autofocus mechanism which utilizes light. One method is called Passive Autofocus which is used for a case where objects to be observed have any patterns. This is to detect with optical detector a maximum point of contrast appearing on an object which is presented by natural illumination light such as sun light and the like and illumination light of observing light source and others of microscope, or to triangulate.
Another is called Active Autofocus used with respect to objects having no pattern, for instance mirror and the like. This method is to project patterns on the object or to project measurement light thereon, and then detect reflection light therefrom with an optical detector.
When the latter Active Autofocus method is used in microscope and the like, conventionally, to easily separate the natural illumination light or the illumination light of the light source from a light for autofocus, or to avoid inconvenience that patterns projected on the object may be seen by an observer, invisible light such as near-infrared light and the like has been used as luminous flux to be projected on the object.
However, general apparatuses such as microscope and others are optically designed for wavelength of visible light area. In the method of using invisible light as projecting light, as mentioned above, when trying to additionally provide autofocus mechanism in such an apparatus, it is necessary to largely reconstruct the optical system of the apparatus so as to adjust the wavelength of the light source for autofocus, causing a demerit of cost of reconstruction increasing accordingly.
To keep the reconstructing cost low, there is the possibility of damaging optical performance that the apparatus originally owns.